The present invention relates to computer-assisted navigation and, more specifically, to a detachable support arm which may be used to couple a computer-assisted navigation reference array to an instrument.
The controlled positioning of surgical instruments is of significant importance in many surgical procedures. Various methods and guide instruments have been developed for properly positioning a surgical instrument. Such instruments and methods include the use of surgical guides which are properly positioned in relation to one or more anatomical structures and function as mechanical guides for surgical instruments such as, e.g., cutting, reaming, and drilling instruments. The use of such surgical guides is common in orthopedic surgical procedures, and such guides may be used to properly locate and align a surgical instrument with respect to a bone when preparing the bone for receiving an implant such as an artificial joint. Positioning relative to the bone has typically been aided by using intramedullary instrument systems. Intramedullary systems utilize instruments placed within the structure of a bone, for example the intramedullary canal. The instruments provide a temporary positioning reference relative to the bone anatomy.
The advent of minimally invasive surgery has increased the requirement for inventive positioning systems to replace intramedullary systems, for example, computer-assisted navigational systems, as described below, and extramedullary frames and alignment devices, such as the one disclosed in “Method and Apparatus for Achieving Correct Limb Alignment in Unicondylar Knee Arthroplasty,” U.S. patent application Ser. No. 10/305,697, filed Nov. 27, 2002, the disclosure of which is hereby incorporated herein by reference.
Computer-assisted navigational techniques often involve acquiring preoperative images of the relevant anatomical structures and generating an anatomical coordinate system database which represents a three-dimensional model of the anatomical structures. The relevant surgical instruments typically have a known and fixed geometry which is also defined in the database preoperatively. During the surgical procedure, the position of the instrument being used and the location of one or more nearby anatomical landmarks are registered with the anatomical coordinate system by employing a position sensing system capable of locating instruments and landmarks in all six degrees of freedom. A graphical display showing the relative position of the instrument and anatomical structures may then be computed in real time and displayed for the surgeon to assist in properly positioning and manipulating the surgical instrument with respect to the relevant anatomical structures.
In such image-guided procedures, a robotic arm may be used to position and control the instrument, or the surgeon may manually position the instrument, and use the display of the relative position of the instrument and anatomical structure to properly position the instrument. Examples of various computer-assisted navigation systems are described in U.S. Pat. Nos. 5,682,886; 5,921,992; 6,096,050; 6,348,058 B1; 6,434,507 B1; 6,450,978 B1; 6,490,467 B1; and 6,491,699 B1. The disclosures of each of these patents are hereby incorporated herein by reference.
Surgical instruments have typically been adapted for use with computer-assisted navigation systems by clamping a position reference array that is registrable in the navigation system onto the surgical instrument at an arbitrary position and orientation relative to the instrument. Because the position and orientation is arbitrary, the geometric relationship between the reference array and the surgical instrument must then be calibrated in order to register the combination of the reference array and the surgical instrument in the navigation system and to properly graphically display the relative position of the instrument to the anatomical structure. Thus, each time the reference array is coupled to a surgical instrument, the combination must again be carefully calibrated and registered to ensure the graphical display viewed by the surgeon on the computer-assisted navigation system reflects the actual position and orientation of the instrument relative to the anatomical structure.
The variability associated with arbitrarily clamping a reference array to a surgical instrument and the possibility of a clamped reference array slipping relative to the surgical instrument causes uncertainty in the geometry of the combination, thus requiring careful and possibly repeated instrument calibrations. Surgical tools which include a reference array permanently affixed eliminate the uncertainty of the geometry and repeated calibration and registration in the navigation system; however, a surgical tool so equipped may then not be suitable for procedures which require the array to be in a different position relative to the instrument or may not be suitable for use without the computer-assisted navigation system because of the reference array that is permanently affixed to it.